The invention relates to an air-conditioning system with a refrigerant circuit which comprises an evaporator, a compressor conveying the refrigerant from a low-pressure side to a high-pressure side, a header arranged on the low-pressure side between the evaporator and the compressor and an internal heat exchanger which has a high-pressure-side heat exchanger duct and a low-pressure-side heat exchanger duct which is in thermal contact with the latter.
Air-conditioning systems of this type are used, in particular, in motor vehicles, for example in the form of CO2 air-conditioning systems. The internal heat exchanger serves for transmitting heat from the refrigerant on the high-pressure side to the refrigerant on the low pressure side, with the result that what is known as the performance number, that is to say the ratio of the refrigerating capacity and the drive power of the air-conditioning system, can be markedly increased.
An air-conditioning system of this type is disclosed in the publicly distributed publication DE 196 35 454 A1. There, the internal heat exchanger is integrated, together with the header, into a structural unit by being accommodated in the interior of a header housing, for example in the form of a flat-tube spiral with turns spaced from one another.
It is known, furthermore, to use as an internal heat exchanger for an air-conditioning system a coaxial tube conduit with two fluid-separated tube longitudinal ducts which are in thermal contact with one another, in order to subcool the high-pressure-side refrigerant upstream of an expansion valve by the transmission of heat to the low-pressure-side refrigerant. The laid-open publication DE 1 208 314 describes a coaxial tube conduit which serves this purpose and in which an inner tube is surrounded concentrically by an outer tube and is provided on the inside with a longitudinal ribbing increasing the heat transmission surface. A wire screw may be introduced between the outer tube and the inner tube in order to lengthen the flow path effective for heat transmission. Inner-tube configurations are also indicated there as known, in which the inner tube is folded in a star-shaped manner or in which a sheet-metal helix for generating a swirl flow is inserted into the inner tube.
An air-conditioning system for a motor vehicle is also known, in which an internal heat exchanger is combined with an evaporator and with an expansion valve to form an integral structural unit. However, such a combination of the internal heat exchanger combining the internal heat exchanger in this way onto or into the evaporator often entails a relatively high construction space requirement, which, particularly under the confined conditions of installation of motor vehicles, may lead to difficulties.
In the older German patent application No. 199 03 833.3 which has not already been published, an integrated header/heat-exchanger structural unit is disclosed, in which the internal heat exchanger is formed by a coiled coaxial tube conduit which is received in the header housing.
The technical problem on which the invention is based is to provide an air-conditioning system of the type initially mentioned, with an internal heat exchanger which can be manufactured relatively simply and, for a given heat transmission capacity, requires relatively little additional construction space.
The invention solves this problem by the provision of an air-conditioning system having the features of claim 1, 3 or 4.
According to one embodiment of the present invention, an air-conditioning system is provided with an internal heat exchanger that contains, in particular, a coaxial tube conduit which has helical webs between an outer tube and an inner tube and/or which is coiled overall at least in portions. The helical webs are integrally formed on the outer tube and/or the inner tube and can therefore be implemented relatively simply in production terms. By virtue of their helical shape, for a given construction length of the coaxial tube conduit, they lengthen the flow path for the refrigerant, for example the low-pressure-side refrigerant, which flows through between the outer tube and the inner tube and which is in thermal contact with the refrigerant, for example the high-pressure-side refrigerant, led through the inner tube. Additionally or alternatively to this measure, the coaxial tube conduit may have a coiled design, with the result that the construction space length required can be kept markedly smaller than the flow path length effective for heat transmission. At the same time, the low-pressure-side heat exchanger duct forms a refrigerant circuit portion between the evaporator and the header and/or between the header and the compressor.
According to another embodiment of the present invention, the coaxial tube conduit is formed by an extruded inner tube with outer webs, which is pushed into an outer tube, or by an extruded outer tube with inner webs, into which the inner tube is pushed, or by a tube extruded in one piece and having integrated webs between the inner and the outer tube.
According to another embodiment of the present invention, the extent of the internal heat exchanger formed by a multiduct tube conduit extends, on the low-pressure side, on both sides of the header, for which purpose the low-pressure-side tube longitudinal duct has a portion issuing into a housing of the header and a portion issuing out of said housing, while the high-pressure-side tube longitudinal duct crosses the header housing as a continuous duct or issues with a first portion into a high-pressure leadthrough space formed within the header housing and issues with a second portion out of said high-pressure leadthrough space. Depending on the configuration within the header housing, there, the issuing-in and/or issuing-out low-pressure-side tube longitudinal duct is in thermal contact with the high-pressure-side tube longitudinal duct or the high-pressure leadthrough space, so that the internal heat exchanger consequently also extends at least partially within the header housing.
According to another embodiment of the present invention, the internal heat exchanger contains a coiled multiduct tube conduit which surrounds the header. In other words, in this case, the header is accommodated in the tube helix of the internal heat exchanger, thus keeping the construction space requirement of the air-conditioning system low.
According to another embodiment of the present invention, the outside of the header is provided with a screw-shaped profile corresponding to the surround multiduct tube conduit helix, so that the latter comes to bear with a form fit against the outside of the header in a guided manner.